This invention relates to a vacuum circuit interrupter and, more particularly, to a vacuum circuit interrupter of the type in which the contacts of the interrupter are located within a metal housing that serves as a portion of the evacuated envelope of the interrupter and is electrically connected to one contact of the interrupter.
We are especially concerned with a vacuum interrupter of this type which is rated for interrupting currents greater than 20,000 amperes (r.m.s. interrupting current with any factor of asymmetry up to a maximum of 1.3). Such currents are typically interrupted by separating a pair of disc-shaped contacts to draw an arc therebetween through which arcing current flows until interruption is completed. It is usually assumed that substantially all the arcing current flows between the contacts. But when high currents in the above 20,000 ampere range are interrupted in the type of vacuum interrupter that comprises disc-shaped contacts and a metal housing connected to one contact and closely surrounding the contacts, this is definitely not the case. More particularly, we have found that frequently 25% or more of the arcing current in such an interrupter will flow between one of the contacts and the surrounding metal housing during interruption of these high currents.
This relatively high arcing current between one contact and the metal housing can cause damage to the interrupter unless special protective measures are taken.